Truffle oil is flavored oil made from truffles. Truffle, one of the rarest and most expensive foods, is a fungus that grows underground near the roots of trees. They are difficult to find, and are routed out by animals, such as pigs and dogs, that have been specially trained. The truffle's appearance is round and irregularly shaped. There are almost 70 known varieties of truffles, the most prized is the black truffle. The white truffle is the most popular. Truffle oil can be used to flavor meat, pasta, risotto, or drizzle some over bruschetta.